1. Field of the Invention
The invention relates, generally, to collator driven ladder chains for use in copiers/duplicators, and more particularly, to a device for and a method of fastening the exposed cable ends of a substantially plastic ladder chain to make a continuous chain thereof.
2. Description of the Prior Art
Heretofore, various techniques for coupling the exposed cable ends of plastic collator driven ladder chains have been employed in the art. These techniques include tungsten inert gas (TIG) and electron beam (E-beam) welding, epoxy bonding and lock collar swedging. Notwithstanding desirable features of each of the foregoing techniques, major problems exist which have been difficult to overcome up to the present time.
For example, metallographic examination of previous TIG and E-beam welded plastic ladder chains, i.e., examination of the interface between the plural steel cables therein and the master cross links, revealed extensive recrystallization, grain growth and networks of carbide precipitates along grain boundaries in a significant zone adjacent to the weld bead. This large heat affected zone (HAZ) was attributable, mainly, to excessive welding times. It was found that the HAZ extended along the steel cable from the weld bead, a distance comparable to the diameter of the cable used, e.g., 0.30 inch. Hence, efforts to minimize welding times by increasing welding currents were employed.
Although metallographic examination, after the foregoing modification, revealed a slight decrease in HAZ lengths, no significant reductions in recrystallization, grain growth, or the degree of carbide precipitation within the HAZ was found. In addition, after static and dynamic force testing, examination of failure fracture surfaces by scanning electron microscopy revealed predominantly brittle and fatigue fractures in many wires of the cable. Moreover, the many surfaces, i.e., between the weld bead, the cable and the master cross link, contained fractured or cracked wires along the outer edges of the cable that were indicative of advanced fatigue. It also was found that brittle and fatigue failures were enhanced by the decomposition of the cable lubricant and remnants of the plastic jacket during the welding process, supplying thereby, an abundant supply of carbon atoms which increased carbide precipitation.
Since careful control and optimization of the primary welding parameters is necessary, as the foregoing indicates when using TIG or E-beam welding, these techniques are deemed unsatisfactory for affixing the exposed cable ends of a plastic ladder chain to make a continuous chain. Although care in manufacturing such a proper cleaning procedures to remove both the lubricant and plastic remnants from the cable prior to welding, will provide additional life time of the connected cable under static pullout tests and dynamic driving force tests, there is a need in the art to eliminate the necessity for sophisticated control and optimization procedures and additional cleaning procedures to fabricate continuous plastic ladder chains having long term life.
As brittle and fatigue failures are characteristic of the foregoing welding techniques, failure due to the cable pullout is characteristic of the well known epoxy bonding technique. In this technique, the failure mechanism was found to be shearing at the epoxy-cable interface. Typical static pullout loads between 25 and 75 pounds and dynamic driving force loads of 3 in-lbs were used in testing this technique as well as the foregoing welding techniques. It was found that each technique withstood, quite well, the static pullout test but failed the more demanding dynamic driving force test after less than 36 hours of continuous loading.
An additional problem encountered with the epoxy bonding technique was the difficulty in restricting the flow of the epoxy prior to setting while still maintaining the proper pitch, i.e., the position of the steel cable in relationship to the master cross link. Thus, there is a need in the prior art to eliminate cable pullout failures due to static and dynamic loading, while maintaining simple manufacturing procedures for affixing the exposed cable ends of a substantially plastic ladder chain together to make a continuous ladder chain thereof.
Another technique used in the prior art, termed the swedge lock collar technique, involves the formation of a conical volume of material which fits around the cable snugly inside a chamfer in the master cross link. As loading is applied to the cable, the aforementioned collar is compressed, thereby applying a uniform compression force on the cable. Although this technique, in operation, appeared to withstand the static and dynamic testing forces aforementioned, a number of difficulties were encountered. These difficulties included slow and tedious assembly, non-uniform cone formations around the cable, separation of the outer wires of the cable during forming of the cone and the inability to consistently form cones with proper tolerances between cross link members.
Consequently, there is a need in the art for a method of affixing the exposed metallic cable ends of a substantially plastic ladder chain, used as a driven chain in a collator, to withstand both the static and dynamic forces experienced in actual operation while eliminating slow and tedious manufacture assembly, maintaining uniformity in manufacture assembly and maintaining proper clearance between cross link members.
The prior art, as indicated hereinabove, includes some advances in affixing the exposed ends of substantially plastic ladder chains to make a continuous chain thereof. However, insofar as can be determined, no prior art device or method incorporates all the features and advantages of the instant invention.